This invention relates to transmission systems using multicarrier modulation. More particularly, the invention relates to multicarrier transmission systems that support multiple applications.
In a conventional multicarrier transmission system, transceivers communicate over a communication channel using multicarrier modulation or Discrete Multitone Modulation (DMT). Carriers or subchannels spaced within a usable frequency band of the communication channel are modulated at a symbol transmission rate of the system. In ADSL (Asynchronous Digital Subscriber Line) systems, the symbol rate is approximately 4 kHz. Every 250 microseconds, the transmitting transceiver allocates a new set of bits for transmission to the subchannels so that the bit error rates of the subchannels are substantially equal at the receiving transceiver. Consequently, for a given symbol period the numbers of bits may vary from subchannel to subchannel.
ITU (International Telecommunication Union) standards G.992.1 and G.992.2 specify parameters that characterize the operation of ADSL DMT transceivers. Examples of parameters, to name but a few, include the data rate (b/s) for the connection between the transceivers, the number of subchannels in the upstream and downstream directions, and the number of bits allocated to each subchannel. In general, such parameters remain fixed after the initial configuration and installation of the transceiver. Some parameters depend on the data rate of the connection and may change when the ADSL connection is at a high or low data rate. Some parameters may change when channel conditions change. However, after the type of application is determined, i.e., voice, data, video, etc., the parameters are optimized and fixed for that application.
For splitterless operation, described in the ITU G.922.2 standard, ADSL transceivers store xe2x80x9cchannel profiles,xe2x80x9d which include a subset of parameters that are used when conditions of the communication channel change (e.g., a telephone goes off the hook). When the channel conditions change because of an event that the ADSL transceiver does not control (e.g., a telephone connected to the same wire as the ADSL transceiver goes off hook), the ADSL transceiver must identify the new channel condition, retrain some of the receiver functions (e.g., equalizers, echo cancellers, etc.), and switch to the channel profile that is used for the new channel condition. This process, defined as a xe2x80x9cFast Retrainxe2x80x9d procedure in ITU G.922.2, takes approximately 1-2 seconds. These channel profiles, however, depend solely on the channel condition and not on the application(s) executing on the ADSL connection.
As technological advances increase the data rate throughput for multicarrier transmission systems, ADSL transceivers are becoming capable of supporting multiple applications. To support multiple applications, it is necessary that the ADSL transceiver be able to quickly and efficiently adapt the transmission parameters as the number and type of active applications change over time. For example, if the ADSL transceiver is accessing data over the Internet when a voice telephone call that is being transported over the ADSL connection becomes active, the ADSL transceiver must be able to modify the transmission parameters to accommodate both active applications. As other voice telephone calls and different applications (e.g., video on demand, video conferencing) become activated and deactivated over the ADSL connection, the ADSL transceiver must also be able to support the various transmission requirements of the various combinations of concurrently active applications. For example, video signals have higher reliability but lesser transmission delay requirements than voice and data signals. For some transmission systems, it has been necessary to find a compromise between high reliability and transmission delay.
Thus, there remains a need for a system and method that can support the various transmission requirements of multiple active applications as the number and type of active applications change over time.
One objective is to provide a DMT transceiver that can support multiple applications and quickly and efficiently modify transmission parameters over time as applications are activated and deactivated. In one aspect of the invention, a multicarrier modulation system has two transceivers in communication with each other over a communication channel. In one aspect of the invention, a multicarrier modulation system has two transceivers in communication with each other over a communication channel. The invention features a method for supporting a plurality of applications. A plurality of application profiles is defined. Each application profile corresponds to a unique set of one or more applications and specifies at least one transmission parameter for each application in that unique application set for transmitting information associated with that application over the communication channel.
The plurality of application profiles is stored at one of the transceivers. Information is transmitted according to a first stored application profile that corresponds to a set of currently active applications. A second stored application profile is selected in response to a change in the set of currently active applications. This second application profile corresponds to the one or more applications in the changed set of currently active applications. The transmission of information transitions to the use of the second stored application profile, without interrupting communication between the transceivers in order to retrain the transceivers.
A message is transmitted to one of the transceivers, identifying the second application profile as the application profile to use for subsequent communications between the transceivers. The message can operate to request a transition to the second application profile. Either a receiver or a transmitter of a transceiver can send the message to initiate the transition.
A reply message is received from the transceiver to which the message was transmitted. When the receiver sent the initial message, the reply message grants the request and synchronizes use of the second application profile. In one embodiment, an inverted sync symbol is used for the reply message. When the transition is transmitter-initiated, the reply message grants the request to transition to the second application profile. Then, another message is sent, acknowledging the grant and synchronizing use of the second application profile. In one embodiment, this other message is an inverted sync symbol.
Each application profile can be transmitted to the other transceiver over the communication channel with or without performing a full initialization of the transceivers. Application profiles can be generated upon an initial occurrence of a unique set of active applications, and associated with that unique application set. In one embodiment, each of the transceivers locally generates at least one of the transmission parameters for one of the stored application profiles using a predefined process employed by both transceivers. In other embodiments, transceivers can be preconfigured with the stored application profiles.
In an application profile, the transmission parameters specified for each application includes at least one of: a transmission data rate, subchannels allocated for downstream and upstream transmission, a number of bits allocated to each of the subchannels, performance margin, fine gain adjustments for each of the subchannels, interleave depth, a minimum and a maximum QAM constellation size, a length of a cyclic prefix, a codeword size, a framing mode, and trellis code.
In another aspect, the invention features a method for supporting multiple applications that are active between the transceivers. A plurality of application profiles is developed for characterizing transmission of information over the communication channel. Each application profile is associated with a unique set of one or more applications that may become active between the transceivers. The application profiles are stored at the transceivers. Information is transmitted over the communication channel according to a first stored application profile that corresponds to a set of currently active applications. A second one of the application profiles that corresponds to the changed set of currently active applications is retrieved in response to a change in the set of currently active applications that are active between the transceivers. The transceivers transition to transmitting information over the communication channel according to the second application profile. The transitioning can occur with or without retraining the transceivers.
In still another aspect, the invention features a method for supporting a plurality of applications in which a plurality of application profiles are defined. Each application profile corresponds to a unique set of one or more applications and specifies at least one transmission parameter for each application in that unique application set for transmitting information associated with that application over the communication channel. The plurality of application profiles is stored at one of the transceivers.
In yet another aspect of the invention, a multicarrier modulation system has a transceiver communicating over a communication channel. A plurality of application profiles is defined. Each application profile corresponds to a unique set of one or more applications and specifies at least one transmission parameter for each application in that unique application set for transmitting information associated with that application over the communication channel.
The plurality of application profiles is stored at the transceiver. Information is transmitted according to a first stored application profile that corresponds to a set of currently active applications. A second stored application profile is selected in response to a change in the set of currently active applications. This second application profile corresponds to the one or more applications in the changed set of currently active applications. The transmission of information transitions to the use of the second stored application profile, without having to retrain the transceiver. The transceiver can transmit or receive a message that identifies the second application profile as the application profile to use for subsequent communications.
In still another aspect of the invention, each application profile corresponds to a unique set of one or more applications and specifies at least one reception parameter for each application in that unique application set, for receiving information associated with that application over the communication channel. The reception of information transitions from using the first stored application profile to use of the second stored application profile without having to retrain the transceiver. Again, the transceiver can transmit or receive a message that identifies the second application profile as the application profile to use for subsequent communications.